The present invention relates to an apparatus for controlling the supply of fuel to an internal combustion engine, and more particularly to such an apparatus of the type using a hot-wire air flow meter.
A hot-wire air flow meter is being developed for measuring the flow rate of intake air into an internal combustion engine to control the supply of fuel into the engine. A constant temperature type hot-wire device is composed of an automatic balancing bridge circuit which measures the flow rate of air passing over a hot wire constituting one branch of the bridge circuit as a change in the electric current flowing through the hot wire. Since, however, the hot wire of this type of flow meter responds very rapidly to a change in the flow rate of the air passing over the wire, fluctuations or pulsations of a high frequency several times as high as the average rotational speed of the engine in the flow of the intake air, which are caused by opening and closing the intake valves of the engine, will create corresponding fluctuations in the output of the flow meter. The output signal of a flow meter of this type is sampled for use in controlling the supply of fuel using an electronic fuel injection device. Thus pulsations in the output signal of the flow meter will cause corresponding fluctuations in the air-fuel ratio. The fluctuations in the air-fuel ratio adversely affect the performance of the engine, the consumption of fuel, the composition of exhaust gas, etc. It is difficult to eliminate the fluctuations which can severely impair the response of a prior art mixture ratio control which detects the concentration of oxygen in the exhaust gas for feedback control, because of a relatively slow response speed of the control.